Surface water, such as lake, stream, canal or river water, or subterranean water, are generally treated in water treatment plants to prepare the water for use as drinking or potable water for human consumption or use, including coagulation, sedimentation, filtration and disinfection processes. This raw or pre-treated water often contains bacteria, pathogens, organic and inorganic substances that can cause a bad taste or odor, or is otherwise not safe for human consumption. For example, the water may contain organic substances from decaying vegetation, or chemicals from various agricultural or industrial applications, such as pesticides and herbicides. These water treatment plants utilize filtration systems to remove suspended solids from the water prior to it being delivered to the end consumer.
Many wastewater treatment plants include a final stage of wastewater treatment usually referred to as a tertiary surface water gravity filter system to prepare the wastewater before returning to the general environment including rivers, lakes, streams or the ocean or for human non-potable reuse purposes such as watering golf courses, lawns and public areas. This final treatment of the wastewater removes suspended solids from the water prior to it reaching the Wetwell, a finished wastewater storage area in the wastewater water plant, before ultimately being delivered to the environment.
These filtration or filter systems can be single, dual or multi-media filters that are designed and built in all types of physical configurations which allow water to flow thru the filter by gravity. The filter systems are designed so that the media in the filters catch sufficient suspended solids in the water as it flows thru the media to reduce the filter effluent (i.e. the water coming out of the filter) turbidity to a predetermined acceptable level (e.g., for human consumption or to be returned to the environment). Over time, the captured suspended solids in the filter's media starts to clog the filter reducing the performance and flow of water out of the filter. Once the filter's performance is reduced to a predetermined low level, the filter must be backwashed to clean them and return them to service for maximum performance. This phenomenon is measured in various ways including increasing filter effluent turbidity, increasing filter headloss, increasing filter level, and a predetermined time duration. If any of these events occur, the filter must be backwashed to return it to maximum performance.
The filters need to be backwashed periodically, sometimes as much as two (2) to three (3) times per week depending on water effluent quality conditions. During the backwash procedure, the treated water used to clean the filter is routed to a wastewater treatment system in the plant such as a clarifier, lagoon, pond and or pumped back to the head of the plant. Typically, this filter backwash wastewater is sent to the treatment plant's wastewater treatment system for processing, treatment and removal. The excess backwash water wasted can be substantial and worth a significant amount of money and reduced production to the treatment plant. Thus, optimizing a filter backwash system's performance can reduce the amount of filter backwash wastewater used during the backwash process thereby increasing plant water production and decreasing plant wastewater treatment while saving money.